Abstract
A stable carbon paste electrode (CPE) was prepared with Th(IV)-hexacyanoferrate (Th-HCF) ion pair and its electrochemical behavior was investigated by cyclic voltammetry. The apparent heterogeneous rate constant, ks, and transfer coefficient, a, for electron transfer between Th-HCF ion-pair and CPE were calculated as 3.1 ± 0.1 s-1 and 0.47, respectively. The surface coverage (Γ) of the proposed electrode was calculated as 7.06 × 10-10 mol cm-2. The proposed Th-HCF modified carbon paste electrode (THMCPE) showed a good electrocatalytic behavior with a significant shift toward negative potentials in oxidation of ascorbic acid (AA) and dopamine (DA) in acidic media (phosphate buffer solution, pH 3). The THMCPE exhibited excellent characteristics for simultaneous determination of AA and DA. Amperometric curves using the catalytic currents are linear for DA and AA concentrations in the ranges 8 × 10-6 - 2 × 10-3 and 1 × 10-5 - 2 × 10-3 mol L-1 with detection limits 5.6 × 10-6 mol L-1 and 4.7 × 10-6 mol L-1, respectively. Diffusion coefficients of AA and DA in electrocatalaytic oxidation were calculated from chronoamperometric data.
Highlights
Modified carbon electrodes have been widely used as sensitive and selective sensors in various electroanalytical methods
The significant negative shift in the peak potential about 330 mV and the enhanced current response observed with the Th-HCF modified CPE (THMCPE) compared to bare carbon paste electrode (CPE) indicate a strong electrocatalytic effect of Fe(CN)63-/Fe(CN)64- redox couple in the THMCPE towards the oxidation of Ascorbic acid (AA)
It should be noted that in contrast with the majority of the electrochemical studies reported in literature for the simultaneous determination of AA and DA, no shift in the potential peaks of AA or DA was observed in all mixed solutions using the proposed modified electrode
Summary
Modified carbon electrodes have been widely used as sensitive and selective sensors in various electroanalytical methods. A major problem is that both AA and DA are oxidized at nearly same potential with poor sensitivity at (unmodified) electrodes, which resulted in overlapped voltammetric responses making their discrimination highly difficult.[43] Electrochemical techniques with modified electrodes have received great interest for neurotransmitters determination in the presence of ascorbic acid as they are more selective and less time consuming and more versatile than those based on other colorimetric or spectrophotometric methods. We prepared a Th-HCF carbon paste electrode and examined its electrochemical behavior using different voltammetric techniques. The carbon paste electrode was prepared by hand-mixing of graphite powder, paraffin and Th-HCF ion-pair.
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